ButtonGroup : Java Glossary

A Swing component that groups together JToggleButtons,
JRadioButtons or JCheckBoxes so
that when one is pushed the others are automatically deselected. The
AWT (Advanced Windowing Toolkit) equivalent is called CheckboxGroup. You use ButtonGroup to define which JRadioButtons
etc. are connected. ButtonGroup does nothing visually. It
is up to you to place the individual buttons, or set them off in such a way it is
clear they are logically connected.